Preliminary experimental studies on particles levitation in air under the effect of wideband ultrasound waves

We investigated the possibility of controlled levitation of particles in the air under the influence of wideband ultrasonic waves. We examined the interference field formed by the radiation of counterpropagating emitters of signals with linear frequency modulation. It is proposed to use two counter-directed emitter arrays focused at the center. The focusing of the emitter arrays is achieved due to the fact that the elements of the arrays are placed on the surface of the sphere in a certain sector. Then the focus point is the center of the sphere at any radiation frequency. When a common-mode wideband signal is applied to all elements of the array, focusing of the wideband signal is achieved in the center of the sphere. When a monochromatic signal is applied, a levitation region elongated along the axis of the system is formed. We consider the case when the distance between the radiating gratings is several times larger than the size of the aperture of the gratings. For wideband signals particles are grouped into a single stable pressure node of standing waves in the center of the system. This provides a single local minimum potential for the selective control of an individual particle. Moreover, a force arises that draws particles into the central region. (paper)